Chain link plates for conventional plate link chains, which are used in particular as drive chains in internal combustion engines, are typically produced in prior art in a two-stage punching process. The link openings and particularly loaded sections of the chain link plate contour, e.g. the plate back sides of simple chain link plates or the tooth flanks of toothed plates, are pre-punched from a sheet metal strip in a coarse manner with a series of different dies and then profiled in a second punching step. During profiling, the contour that is pre-cut with oversize in a coarse manner is punched to its final dimension in a profile cut, where the small machining width of the profile cut enables a smooth-cut portion which extends far beyond half of the cut surface of the punched-out contour. By profiling the link openings and other contours of the chain link plates subject to wear, the formation of microscopic cracks in the smooth-cut portion is prevented and the tear-free smooth-cut portion of the cut surface is significantly increased, thereby improving wear resistance and durability of the chain link plates.
Such a method for pre-punching and profiling chain link plates is described in DE 10 2004 021 695 A1. Only the portions of the link openings to be profiled and the contour of the toothed plates are there first punched out from a sheet metal strip, so that the plate that is pre-punched in a coarse manner is still firmly connected to the sheet metal strip in the curved face side regions. For improving positioning of the sheet metal strip and parallelism of the profiled surfaces, all sections of the chain link plate contour to be profiled are then punched out to their final dimensions in a second work step by profiling in the reverse order and punching direction. In a final step, the chain link plates are ultimately separated from the sheet metal strip at the curved face side regions by punching them out or blanking them.
The high performance chains used particularly in the field of automotive technology are exposed to high loads and dynamic load changes at high speeds and sometimes to an aggressive environment. Accordingly, it is important for such high performance chains that the functional surfaces in the region of the tooth flanks, plates, rear surfaces and pin openings exhibit low surface roughness, which can generally only be achieved by profiling or fine blanking. In automotive drives, such plate link chains typically run along guide and/or tensioning rails, for which reason, in particular, the plate back sides of the chain link plates must exhibit low surface roughness in order to obtain a suitable service life not only for the plate link chain but also for the associated rails.
Toothed chains are used in automotive drives in addition to simple non-toothed bush or roller chains, where the tooth contour of the toothed plates as a functional surface is also subjected to a profiling process or fine blanking. In addition to the tooth contour, also the plate back side is commonly fine punched or profiled in the case of such toothed plates, in order to obtain a desired surface quality. Such a profiled toothed plate is described, for example, in DE 20 2007 002 046 U1.
The production of toothed or non-toothed chain link plates for high-performance chains is typically effected from a steel sheet which is fed as a sheet metal strip to a punching machine. The chain link plates are punched out from this sheet metal strip in several punching steps, where the longitudinal axes of the chain link plates are typically aligned parallel to the longitudinal edge of the sheet metal strip and several punch tracks are commonly provided. A common punching method comprises e.g. eight punch tracks above one another. For example, an advance length of at least 17 mm is used with a straight chain link plate for a chain with a chain pitch of 8 mm and a plate length of 15.55 mm, where the distance between two consecutively arranged plates in such an embodiment is 1.45 mm and the distance between two punch tracks is approx. 2.25 mm. These distances are necessary in order to be able to form sufficiently stable dies that are inserted between the plate blanks and there punch away the waste material. In addition, a certain edge spacing from the edge of the sheet metal strip must be maintained so that considerable punching waste arises despite several punch tracks above one another.
A method for the production of high-performance chain link plates is known from DE 10 2013 002 263 A1 having a reduced punching waste. In this method, the feed length is reduced and preferably limited to a value just below twice the pitch. As a result, the face side head portions are connected after punching and are separated by a subsequent separation cut, so that the punch web otherwise typical in punching is eliminated. Since the surface roughness of the contour on the face side portions of the chain link plate is of minor importance, the separation edges and protruding burrs resulting from the separation by way of a separation cut are acceptable The same applies to the tips of the teeth of toothed plates which do not engage with the sprockets, regardless of the design and configuration of the toothed chain. In contrast, both the pin openings and the plate back sides, and also the front side sections of straight chain link plates as well as the outer flanks and inner flanks of toothed plates are provided with a high surface quality with the respective two-stage punching methods. The connection of the tooth tips of mutually facing tooth contours there serves a more accurate profiling process of the tooth flanks. Despite the reduced advance distance, the number of chain link plates producible from a sheet metal strip can be increased only slightly with this method.